Reward grows in case of Tennessee woman missing a week

Tennessee's top investigator says there is no suspect, as the search continues

Singer Whitney Duncan says of her cousin: "When you see Holly, you see a smile"

Tune in to "Nancy Grace" tonight at 8 ET on HLN for a live update from Holly Bobo's home.

(CNN) -- One week ago Wednesday, a Tennessee nursing student was reported missing. Officials are hoping an increased reward will spring a major break in the search.

The Tennessee Sheriffs' Association added $5,000 Tuesday, bringing the total for information leading to an arrest and conviction in the disappearance of Holly Bobo to $80,000.

It said the investigation continued Tuesday, with road canvasses on five roads leading in and out of Bobo's residence.

Tennessee Bureau of Investigation Director Mark Gwyn said Monday that there's no "person of interest" in the case, which has rocked largely rural Decatur County since 20-year-old Bobo went missing.

"There's a family out there that needs closure, and it's up to us to give it to them," Gwyn said in the town of Parsons, where law enforcement and volunteers have been headquartered.

In addition, law enforcement officers are going door-to-door talking to people near the Bobo's home. The Tennessee Wildlife Resource Agency offered "sight-imaging" technology so investigators can scan the bottoms of nearby lakes.

Bobo was on her way to nursing classes at the Tennessee Technology Center campus in Parsons when her brother saw a man in camouflage leading her from their Darden home into the woods, said John Mehr, special agent in charge for the Tennessee Bureau of Investigation.

The missing woman's cousin, Whitney Duncan -- a country music singer who gained national fame as a finalist on USA Network's "Nashville Star" reality competition -- went online Monday to sharply dispute speculation that Bobo's brother has anything to do with the disappearance.

"My cousin Clint, Holly's brother, is NOT a suspect & I'm sick of people saying that he is," Duncan wrote Monday on her Twitter feed. "He has been cleared for good reason. Shut up."